There could be any number of reasons.
If you wear scents, mosquitoes will like you more. If you sweat a lot, they will like you more. If you do not get enough B Complex vitamins, they will like you more.
As others have said, they are attracted to sweat and the carbon dioxide you exhale. Its how they find food.
Garlic pills might help keeping mosquitoes away.
They like the tasty blood
Because you have blood in your body.
